Mask-frame captivator



L. J. LEWINSON MASK-FRAME CAPTIVATOR July 8, 1969 Sheet Filed Sept. 12,1958 INVENTOR .n 6 W e Lfl J m 5 m 0% L ATVTY.

July 8, 1969 L. J. LEWINSON MASK-FRAME CAPTIVATOR Sheet Filed Sept. 12.1968 INVENTOR Lafhar J. Lew/nson #4: gum e52 ATTY.

United States Patent 01 has 3,454,813 Patented July 8, 1969 3,454,813MASK-FRAME CAPTIVATOR Lothar J. Lewinson, Oak Park, Ill., assignor toAdmiral Corporation, Chicago, 111., a corporation of Delaware FiledSept. 12, 1968, Ser. No. 759,298 Int. Cl. H01j 1/96 [1.5. Cl. 313-284 7Claims ABSTRACT OF THE DISCLOSURE This invention relates to colortelevision picture tubes of the type having an aperture mask throughwhich beams of electrons pass before striking the phosphor screen on\the inner surface of a glass panel, and bimetallic expansion bracketswhich maintain alignment between the mask and the panel over theoperating temperature range of the picture tube. In particular, thisinvention provides captivating means for constraining a plurality ofleaf springs, secured between the expansion brackets and the glasspanel, within their elastic limits in the event the picture tube issubjected to mechanical shock.

In picture tubes of the type described, three mounting studs aretriangularly disposed about the perimeter of the glass panel. A metalframe supporting a multi-apertured shadow mask is releasably secured tothe panel by three apertured leaf springs which cooperate with theappropriate mounting studs. A mosaic of red, blue and green colorphosphors is deposited on the interior of the glass panel in accordancewith conventional lighthouse techniques, using the detachable mask forexposing appropriate portions of the panel to sensitizing light rays.

A tri-gun electron source is mounted in a delta configuration in theneck of a tapered glass envelope which is frit sealed to the glasspanel. The electron guns are mechanically prealigned with respect to theshadow mask such that electrons passing through the apertures impingeonly corresponding color phosphors. For example, electrons emanatingfrom the first gun strike only the red phosphors, electrons from thesecond gun strike only the blue phosphors, etc.

As is well-known, most of the electrons in the electron beam areintercepted by the shadow mask and fail Ito reach the phosphor screen.Since the kinetic energy of these electrons is transformed into heat,the shadow mask undergoes considerable thermal expansion. Uponexpansion, alignment between the electron beams and the correspondingcolor phosphors is upset and, as a result, electrons emanating from thefirst gun may, for example, partially excite the blue or the greenphosphors causing substantial color impurities.

Numerous methods have been suggested for compensating for the thermalexpansion of the shadow mask. One structure incorporates threesubstantially L shaped bimetallic expansion brackets which are securedbetween the frame and corresponding leaf springs. As the temperature ofthe mask-frame assembly increases due to electron bombardment, theexpansion brackets undergo corrective flexures moving the mask-frameassembly closer to the glass panel. Such movement maintains registrationbetween the electrons passing through the shadow mask and thecorresponding color phosphors, thereby helping to assure chromaticpurity over the operating temperature range of the picture tube. For acomplete description of a system of this type, see the copendingapplication of Cowles et al., Ser. No. 742,651, filed July 5, 1968.

During shipping and handling, both before and after installation in areceiver, picture tubes are often subjected to severe mechanical shockcausing the springmounted frame assembly to move with respect to theglass panel. With the implementation of the relatively flexibleexpansion brackets described above, this movement tends to beexaggerated. The frame, being relatively heavy, exerts large forces onthe springs, often inducing permanent deformations therein. Thesedeformations may prevent the frame assembly from returning to itsoriginal position, thereby upsetting mask-panel alignment and causingsubstantial color impurities.

This invention provides captivating means which constrane the leafsprings within their elastic limits, while permitting unimpeded movementof the mask-frame assembly over the entire range of temperaturesencountered during picture tube operation and fabrication. For example,during manufacture, when the glass envelope is frit sealed to the glasspanel, temperatures approach 450' C., and for reasons previouslydiscussed, the bimetallic expansion brackets flex considerably and movethe maskframe assembly substantially. The captivators do not interferewith this normal movement, thus precluding the possibility of inducingstresses in the frame, springs or bimetallic brackets during processing.

Further, the captivators are accurately positioned on the frame withrespect to the corresponding leaf springs, such that, as explainedlater, proper separation between the spring and the captivator isassured, notwithstanding dimensional variations in the springs.Accordingly, three captivators, each comprising a base plate having apair of tabs extending perpendicularly therefrom, are located on themask-supporting frame of the picture tube such that the correspondingleaf springs are properly constrained between the captivator tabs. Thisarrangement allows great flexibility in placement of the captivators andfacilitates the practice of the spring location techniques set out inthe above mentioned copending application.

Thus, the primary object of this invention is to provide an improvedcolor television picture tube.

Another object of this invention is to provide improved means forconstaining the leaf springs in a color television picture tube withintheir elastic limits, in the event the tube is subjected to mechanicalshock.

A further object of this invention is to provide, in a color tube with athermally compensated mask-frame assembly, captivating means permittingfree movement thereof during tube operation and fabrication, whileconstraining the leaf springs within their elastic limits in the eventof mechanical shock.

A feature of this invention resides in means for accurately locating andsecuring the captivator to the masksupporting frame of a colortelevision picture tube with respect to the position of thecorresponding leaf springs, notwithstanding dimensional variations inthe springs.

Other objects, features and advantages of this invention will be seenupon reading the following specification in conjunction with thedrawings in which:

FIG. 1 is a sectional view of a color television picture tubeincorporating the invention;

FIG. 2 is a sectional view taken along line 22 of the color televisionpicture tube shown in FIG. 1;

FIG. 3 is an enlarged view of the upper portion of the color televisionpicture tube of FIG. 2 showing the elements of the invention;

FIG. 4 is a view of the structures of FIG. 2 taken along the line 44showing the relative location of the elements of the invention; and

FIG. 5 is a perspective view of mounting and welding apparatus foraccurately locating and securing the captivator to the mask-supportingframe of thecolor television picture tube in accordance with theinvention.

Referring now to FIG. 1, a color television picture tube includes aglass panel 11 having a spherical contour on which a mosaic 12 of red,blue and green color phosphors is deposited. Three mounting studs 13(best seen in FIG. 2) are accurately embedded or otherwise permanentlysecured to the inside perimeter of glass panel 11. A shadow mask 14,secured to a relatively heavy frame 15, has a spherical contour similarin shape to glass panel 11. Frame 15 has an L shaped cross section and,as explained in the description of FIG. 2, is releasably secured to theglass panel at mounting studs 13.

A glass funnel 16, including a neck portion having three electron guns17 mounted therein, is secured to glass panel 11 by a conventionalcircumferential glass to glass frit seal 18. Electron guns 17 aremechanically prealigned such that electrons emanating therefrom strikecorresponding ones of the different color phosphors forming mosaic 12.Color selection is performed by the wellknown masking effect of shadowmask 14.

In FIG. 2, three mounting assemblies 20, each comprising a leaf spring21 fastened at one end to an L shaped thermal expansion bracket areshown. These assemblies are preferably fabricated and located inaccordance with the teachings of the above mentioned copendingapplication. Three captivators each comprise a base plate 31 having apair of tabs 32 and 33 (best seen in FIG. 3) extending perpendicularlytherefrom. As explained below, captivators 30 are accurately secured toframe 15 such that spring 21 properly extends between tabs 32 and 33.

In FIG. 3, leaf spring 21 includes a front edge 24, a rear edge 23 and astud engaging aperture 22. Captivator 30 is secured to frame 15 suchthat tabs 32 and 33 straddle edges 23 and 24 of the spring. The variouselements are secured to each other by welding. For example, bimetallicexpansion bracket 25 is secured to frame 15 by spot welding, as isspring 21 and bimetallic bracket 25. For details regarding thearrangement and order of assembly of these parts, reference is againmade to the above mentioned copending application of Cowles et al.

In FIG. 4, the location of the various parts with reference to mountingstud 13 (shown in section) is clearly depicted. The distance D is thatbetween the center of mounting stud 13 (also aperture 22 of the leafspring) and the tab edge of captivator 30. This distance is criticalsince, during movement of frame 15 and its attached parts (bracket 25and captivator 30), spring 21 pivots about mounting stud 13. The actualdistance any point on the spring moves is a function of its distancefrom the pivot point, namely the center of stud 13.

The distance F is that between front edge 24 of spring 21 and tab 33.The distance R is that between rear edge 23 of spring 21 and tab 32.These distances must be selected precisely and must be greater than thenormal movement attributable to the deflection of expansion bracket 25during tube processing, and less than that which will produce injurioustorsional forces on the bracket and spring in the event of mechanicalshock. In practice, the distance F is much greater than R since tubeprocessing and operating temperature changes cause frame movement towardthe phosphor screen (to the left in FIG. 4). Thus distances F and R areselected to allow complete freedom of movement of the mounting springsunder all operating and processing temperatures to preclude thedevelopment of injurious stresses which would adversely affectmask-screen registration. Ideally, in normal usage, captivator tabs 32and 33 should never contact spring edges 23 and 24. The captivators solepurpose is to prevent damage in the event of abnormal conditionsoccurring, such as dropping or violent jarring of the tube or completetelevision receiver.

In FIG. 5, there is shown a mounting apparatus 40, comprising anadjustable locating assembly 41, resiliently secured by a pair of springloaded studs 48, to a rigid arm 50, for accurately and automaticallypositioning and mounting the captivator. Arm 50 is pivotably mounted toa pin 51, and spring loaded studs 48 allow only vertical movement ofassembly 41 with respect to arm 50. Adjustable locating assembly 41includes a guide piece 42 having a pair of ram surfaces 43 terminatingin a seating surface 44, and a pair of abutting surfaces 45. Locatingassembly 41 further includes locating means 46 having two perpendicularspaced tab engaging surfaces 47, the distance between surfaces 47 beingvery slightly smaller than the distance between tabs 32 and 33 ofcapitvator 30.

The above structure is mounted on a welding fixture (notshown) havingthree locating pins 61 (only one of which is shown), accuratelypositioned with respect to pivot pin 51. The three locating pins 61extend through corresponding locating holes in frame 15 and expansionbrackets 25 as fully explained in the above mentioned copendingapplication of Cowles et al. In accordance with said application, afixed coordinate distance is maintained between each spring aperture 22and corresponding locating pin 61 once brackets 25 are secured to frame15.

In operation, mounting apparatus swivels about pin 51 until leaf spring21 cooperates with one of the ramp surfaces 43. Locating assembly 41vertically adjusts as the engaged ramp surface 43 is guided by theengaged edge of leaf spring 21, assuring mating engagement betweenseating surface 44 and the flat surface of the leaf spring regardless ofvariations in the positioning of the leaf spring. During this operation,surface 44 depresses the leaf spring somewhat.

Captivator 30 is then positioned between the side of frame 15 and theundersurface of spring 21 with tabs 32 and 33 straddling tab engagingsurfaces 47 and moved until the tabs engage abutting surfaces 45. Thecaptivator may be temporarily held in this position by any of a numberof well-known means, for example, by tiny magnets embedded in surfaces45. The attainment of distances F and R between the captivator tabs 33and 32 and the respective edges 24 and 23 of leaf spring 21 may beautomatically assured by fabricating locating assembly 41 with theproper vertical displacement between the edges of seating surface 44 andtab engaging surfaces 47.

Welding electrodes 53 are then moved, by means not shown, intoengagement with the captivator to secure it to the frame. As should beobvious, the distance D may be predetermined by the placement ofabutting surfaces 45, once the relative positioning between locating pin'61 and pivot 51 is fixed.

In the event the completed picture tube is subjected to severemechanical shock, the mask-frame assembly tends to move along thetransverse axis of the tube. Before excessive deformation of the springsor bimetallic brackets occur, however, the springs engage the captivatortabs, thus restraining further movement. When the maskframe assemblyundergoes movement in response to the thermal expansion of thebimetallic brackets, whether in actual operation or in processing of thetube, the maskframe assembly is not restrained since the distances F andR provide sufficient clearance between the captivator tabs andcorresponding leaf springs. As a result, free movement of the mask-frameassembly is assured over the operating and processing temperaturesexperienced by the picture tube while protection from mechanical shockis provided.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A color television picture tube comprising: a glass panel; aplurality of mounting studs disposed about the interior of said panel; aheavy, rigid frame; a plurality of thermal expansion members secured tosaid frame;

a corresponding plurality of leaf springs secured to said expansionmembers and cooperating with said mounting studs for releasablymaintaining said frame a fixed distance from said panel; and a pluralityof captivating members, accurately positioned on said frame with respectto said leaf springs, confining said leaf springs to flexures withintheir elastic limits in the event said picture tube is subjected tomechanical shock.

2. A color television picture tube comprising: a glass panel; aplurality of mounting studs disposed about the interior of said panel; aheavy, rigid frame; a plurality of thermal expansion brackets,undergoing fiexures in response to variations in temperature, secured tosaid frame; a corresponding plurality of leaf springs, each having afirst end fastened to respective ones of said expansion brackets, and asecond end, including an aperwith respect to said leaf springs to allowfree movement between said frame and said studs over the normal range oftemperatures encountered, 'but restraining said leaf springs tomovements within their elastic limits in the event of mechanical shock.

3. A color television picture tube as set forth in claim 2, wherein eachcaptivating member comprises a base plate including a first tab and asecond tab extending substantially perpendicular to one end thereof;said captivating members being positioned on said frame such that saidtabs straddle corresponding ones of said leaf springs.

4. A color television picture tube as set forth in claim 3, wherein,during tube processing, said thermal expansion brackets are subjected toa maximum temperature and experience maximum flexures, moving said framea corresponding maximum distance with respect to said glass panel; andwherein said leaf springs each include a first edge; said first tabs ofcorresponding ones of said captivating members being spaced from saidfirst edges a first distance great enough to allow said frame to freelymove said maximum distance, but small enough to engage and restrain saidfirst edges in the event of excessive mechanical shock.

5. A color television picture tube as set forth in claim 4, wherein eachof said leaf springs includes a second edge; said second tabs ofcorresponding ones of said captivating members being spaced from saidsecond edges by an amount less than said first distance.

6. A color television picture tube as set forth in claim 4, wherein thespacing between any selected one of said mounting studs and an imaginaryline joining the tabs of its corresponding captivating member defines asecond distance; and wherein the spacing between said one mounting studand the point of attachment of its, corresponding leaf spring andexpansion bracket defines a third distance; the ratio of said firstdistance to said second distance being slightly greater than the ratioof said maximum distance to said third distance.

7. In combination: a glass panel; a plurality of mounting studs disposedabout the interior of said panel; a heavy, rigid frame; a plurality ofthermal expansion brackets, undergoing fiexures in response totemperature variations, secured to said frame; a corresponding pluralityof flat leaf springs each having a first end fastened to said expansionbrackets, and a second end forming an aperture for releasable engagementwith respective ones of said mounting studs; said mounting studs, flatleaf springs and expansion brackets cooperating to maintain said framein registration with said glass panel; said expansion brackets, beingsubjected to high temperatures during tube fabrication and moving saidframe a maximum distance toward said glass panel; and a plurality ofcaptivating members, each comprising a flat plate having a pair of tabsextending substantially perpendicular to said plate; said captivatingmembers being secured to said frame with said tabs straddling respectiveones of said fiat leaf springs; first ones of said tabs being spacedfrom first respective edges of said springs 21 first distance greatenough to allow uninhibited movement of said frame toward said glasspanel over said maximum distance; second ones of said tabs being spacedfrom second respective edges of said springs a second distance which isless than said first distance; said first and said second distancesdefining the maximum movement of said springs under mechanical shockconditions to prevent deformation thereof.

References Cited UNITED STATES PATENTS 2,727,172 12/ 1955 Mark et al 3132,824,989 2/ 1958 Christofferson 31385 3,370,194 2/ 1968 Schwartz et al.3 l392 JAMES W. LAWRENCE, Primary Examiner.

V. LAFRA-NCHI, Assistant Examiner.

US. Cl. X.R. 313-85, 292

